There are bots that buy automatically.

I've been trying to buy The Red Nightmare. I've lowered the price to 12 Divines, but every time the price goes up and the search alert pops up, a level 1 assassin named "klklklklklkllkklkl" shows up and takes everything. It can't be that he has the fastest click; I've spent all day trying to buy it, and the four times I've logged in before, he gets it first and disappears.

Do not know about the specific user you mention, but some of the bots are so good that they buy the item before it even pops up in your search giving you absolutely no chance.

Besides bots there is 1 more issue and that are loading times for different realms. I'm often first to click but then i gotta wait 5minutes to connect to some 90000ping realm, i'm sure this could be done more reasonable way.

Bots were a thing even before this trade change, they had to whisper the user ofcourse, so they had lower chance to actually buy things because the user would get spammed with messages and understand something is not right.